This invention relates to a dynamic random access memory (RAM) and a semiconductor device and more particularly to an effective technology using a so-called one cross point method where a dynamic memory cell is arranged at a cross point of a word line and a bit line.
According to the search done after this invention was made, some inventions which might be related to the present invention described later as an open bit line type (or one cross point method) dynamic RAM were found, including Japanese Patent Laid-Open No. 206991/1988 (related art 1, hereinafter), Japanese Patent Laid-Open No. 13290/1989 (related art 2, hereinafter), U.S. Pat. No. 5,608,668 (related art 3, hereinafter), and Japanese Patent Laid-Open No. 41081/1993 (related art 4, hereinafter). According to related arts 1 and 2, one sense amplifier is fitted into a pitch for two bit lines by positioning sense amplifiers alternately based on the open bit line method (one-cross point method). According to related arts 3 and 4, there is provided a circuit for achieving, based on an electrical model which is substantially the same as a bit line, a reference voltage required for an operation by a sense amplifier provided at an end portion in case where sense amplifiers are positioned alternately for more efficient use of a chip area as in the related arts 1 and 2.
Due to process variations, which will be increased with an increase in micronization of elements, operational conditions would differ largely between a sense amplifier at the end portion and a sense amplifier to which bit lines are equipped on both sides. Thus, according to reviews by the inventor hereof, it was found out that the operational stability would be important more and more. In the related arts 1 and 2, no considerations are made for the arrangement at the end portion in case where sense amplifiers were arranged alternately with respect to bit lines.
Further, cost reduction has been desired for the dynamic RAM (DRAM, hereinafter). In order to achieve the cost reduction, reducing chip sizes may be the most effective. The size of a memory cell has been reduced by promoting its micronization. However, it will be necessary to further reduce the cell size by changing the operating method of memory arrays from now on. By changing the memory array operating method from the two cross point method to the one cross point method, the cell size can be reduced 75% ideally based on the same design rule. In order to achieve the cell size reduction more effectively, the inventor hereof considered effective uses of memory cells provided at the end portion and the reduction of their occupying area when the sense amplifiers are arranged alternately in the memory array according to the one cross point method as described above.
It is an object of the present invention to provide a DRAM and a semiconductor device based on the one cross point method which can attempt improvement of operational margins and reduction of a chip area. The above and other objects and new features of the present invention will be apparent from the description in this specification and with reference to the accompanying drawings.
An outline of a typical aspect of the present invention disclosed herein may be described in brief as follows: There is provided a plurality of memory mats including a plurality of bit lines, a plurality of word lines, and a plurality of memory cells coupled to the plurality of bit lines and the plurality of word lines, the plurality of memory mats being placed in a direction of the bit line, and a sense amplifier array including a plurality of latch circuits being provided in areas between the memory mats placed in the bit line direction, respectively, a pair of input/output nodes of which is connected to half of bit lines provided in the memory mats. In this case, for a general memory mat other than both end portions in the bit line direction, word lines in any one of the memory mats are activated while, for end memory mats provided on the both end portions in the bit line direction, word lines of the both memory mats are activated together.